AP_Logger: ensure that we don't read the same block more than once, dramatically increasing performance.

libraries/AP_Logger/AP_Logger_Block.cpp

@@ -183,13 +183,12 @@ bool AP_Logger_Block::_WritePrioritisedBlock(const void *pBuffer, uint16_t size,
 // read from the page address and return the file number at that location
 uint16_t AP_Logger_Block::StartRead(uint32_t PageAdr)
 {
-    df_Read_PageAdr   = PageAdr;
-
     // copy flash page to buffer
     if (erase_started) {
+        df_Read_PageAdr = PageAdr;
         memset(buffer, 0xff, df_PageSize);
     } else {
-        PageToBuffer(df_Read_PageAdr);
+        PageToBuffer(PageAdr);
     }
     return ReadHeaders();
 }
@@ -239,14 +238,15 @@ bool AP_Logger_Block::ReadBlock(void *pBuffer, uint16_t size)
         df_Read_BufferIdx += n;
 
         if (df_Read_BufferIdx == df_PageSize) {
-            df_Read_PageAdr++;
-            if (df_Read_PageAdr > df_NumPages) {
-                df_Read_PageAdr = 1;
+            uint32_t new_page_addr = df_Read_PageAdr + 1;
+            if (new_page_addr > df_NumPages) {
+                new_page_addr = 1;
             }
             if (erase_started) {
                 memset(buffer, 0xff, df_PageSize);
+                df_Read_PageAdr = new_page_addr;
             } else {
-                PageToBuffer(df_Read_PageAdr);
+                PageToBuffer(new_page_addr);
             }
 
             // We are starting a new page - read FileNumber and FilePage

libraries/AP_Logger/AP_Logger_Block.h

@@ -62,6 +62,7 @@ protected:
 
     uint8_t *buffer;
     uint32_t last_messagewrite_message_sent;
+    uint32_t df_Read_PageAdr;
 
 private:
     /*
@@ -95,8 +96,7 @@ private:
 
     // state variables
     uint16_t df_Read_BufferIdx;
-    uint32_t df_PageAdr;
-    uint32_t df_Read_PageAdr;
+    uint32_t df_PageAdr;    // current page address for writes
     // file numbers
     uint16_t df_FileNumber;
     uint16_t df_Write_FileNumber;

libraries/AP_Logger/AP_Logger_DataFlash.cpp

@@ -219,8 +219,17 @@ void AP_Logger_DataFlash::PageToBuffer(uint32_t pageNum)
     if (pageNum == 0 || pageNum > df_NumPages+1) {
         printf("Invalid page read %u\n", pageNum);
         memset(buffer, 0xFF, df_PageSize);
+        df_Read_PageAdr = pageNum;
         return;
     }
+
+    // we already just read this page
+    if (pageNum == df_Read_PageAdr && read_cache_valid) {
+        return;
+    }
+
+    df_Read_PageAdr = pageNum;
+
     WaitReady();
 
     uint32_t PageAdr = (pageNum-1) * df_PageSize;
@@ -230,6 +239,8 @@ void AP_Logger_DataFlash::PageToBuffer(uint32_t pageNum)
     send_command_addr(JEDEC_READ_DATA, PageAdr);
     dev->transfer(nullptr, 0, buffer, df_PageSize);
     dev->set_chip_select(false);
+
+    read_cache_valid = true;
 }
 
 void AP_Logger_DataFlash::BufferToPage(uint32_t pageNum)
@@ -238,6 +249,12 @@ void AP_Logger_DataFlash::BufferToPage(uint32_t pageNum)
         printf("Invalid page write %u\n", pageNum);
         return;
     }
+
+    // about to write the cached page
+    if (pageNum != df_Read_PageAdr) {
+        read_cache_valid = false;
+    }
+
     WriteEnable();
 
     WITH_SEMAPHORE(dev_sem);

libraries/AP_Logger/AP_Logger_DataFlash.h

@@ -43,6 +43,7 @@ private:
     uint32_t erase_start_ms;
     uint8_t erase_cmd;
     bool use_32bit_address;
+    bool read_cache_valid;
 };
 
 #endif // HAL_LOGGING_DATAFLASH_ENABLED

libraries/AP_Logger/AP_Logger_W25N01GV.cpp

@@ -198,9 +198,17 @@ void AP_Logger_W25N01GV::PageToBuffer(uint32_t pageNum)
     if (pageNum == 0 || pageNum > df_NumPages+1) {
         printf("Invalid page read %u\n", pageNum);
         memset(buffer, 0xFF, df_PageSize);
+        df_Read_PageAdr = pageNum;
         return;
     }
 
+    // we already just read this page
+    if (pageNum == df_Read_PageAdr && read_cache_valid) {
+        return;
+    }
+
+    df_Read_PageAdr = pageNum;
+
     WaitReady();
 
     uint32_t PageAdr = (pageNum-1);
@@ -224,6 +232,8 @@ void AP_Logger_W25N01GV::PageToBuffer(uint32_t pageNum)
         dev->transfer(cmd, 4, nullptr, 0);
         dev->transfer(nullptr, 0, buffer, df_PageSize);
         dev->set_chip_select(false);
+
+        read_cache_valid = true;
     }
 }
 
@@ -234,6 +244,11 @@ void AP_Logger_W25N01GV::BufferToPage(uint32_t pageNum)
         return;
     }
 
+    // just wrote the cached page
+    if (pageNum != df_Read_PageAdr) {
+        read_cache_valid = false;
+    }
+
     WriteEnable();
 
     uint32_t PageAdr = (pageNum-1);

libraries/AP_Logger/AP_Logger_W25N01GV.h

@@ -42,6 +42,7 @@ private:
     bool flash_died;
     uint32_t erase_start_ms;
     uint16_t erase_block;
+    bool read_cache_valid;
 };
 
 #endif // HAL_LOGGING_DATAFLASH_ENABLED